1. Field of the Invention
This invention relates to stir welding methods. More specifically, the invention is a stir welding method utilizing pulsed ultrasonic energy.
2. Description of the Related Art
Stir welding is a form of welding that utilizes a small stir pin to mix abutting or faying surfaces of two pieces of material (e.g., metal materials) to thereby form a joint between the two pieces of material. The materials must be heated into a plastic state where they abut prior to being “stirred.” There are several ways to achieve such heating. In one type of stir welding known as friction stir welding (FSW), a pin tool includes a larger diameter shoulder and a smaller diameter threaded pin. The entire pin tool is rotated and the rotating pin is driven axially into the weld joint until the rotating shoulder comes into contact with the material surface. The rotating shoulder generates frictional energy/heat as it rotates on the material surface to thereby heat the material into its plastic state. The high rotation rates needed to generate the frictional forces, as well as the frictional forces, tend to wear out the pin tool in relatively short periods of time especially when joining thick sections of temperature-resistant alloys such as titanium and steel.